Added DataLayer and ServiceLayer

DataLayer/DataLayer.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp2.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="2.0.1" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.Relational" Version="2.0.1" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\GenericLibsBase\GenericLibsBase.csproj" />
+  </ItemGroup>
+
+</Project>

DataLayer/Dtos/OrderBooksDto.cs

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+// Copyright (c) 2018 Jon P Smith, GitHub: JonPSmith, web: http://www.thereformedprogrammer.net/
+// Licensed under MIT licence. See License.txt in the project root for license information.
+
+using System;
+using DataLayer.EfClasses;
+
+namespace DataLayer.Dtos
+{
+    public struct OrderBooksDto
+    {
+        public int BookId { get; }
+        public Book ChosenBook { get; }
+        public short numBooks { get; }
+
+        public OrderBooksDto(int bookId, Book chosenBook, short numBooks) : this()
+        {
+            BookId = bookId;
+            ChosenBook = chosenBook ?? throw new ArgumentNullException(nameof(chosenBook));
+            this.numBooks = numBooks;
+        }
+    }
+}

DataLayer/EfClasses/Author.cs

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+// Copyright (c) 2018 Jon P Smith, GitHub: JonPSmith, web: http://www.thereformedprogrammer.net/
+// Licensed under MIT licence. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+
+namespace DataLayer.EfClasses
+{
+    public class Author
+    {
+        public const int NameLength = 100;
+
+        //used by EF Core
+        private Author() { }
+
+        public Author(string name)
+        {
+            Name = name;
+        }
+
+        public int AuthorId { get; private set; }
+
+        [Required]
+        [MaxLength(NameLength)]
+        public string Name { get; private set; }
+
+        //------------------------------
+        //Relationships
+
+        public ICollection<BookAuthor>
+            BooksLink
+        { get; set; }
+    }
+
+}

DataLayer/EfClasses/Book.cs

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+// Copyright (c) 2018 Jon P Smith, GitHub: JonPSmith, web: http://www.thereformedprogrammer.net/
+// Licensed under MIT licence. See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.Linq;
+using GenericLibsBase;
+using Microsoft.EntityFrameworkCore;
+
+namespace DataLayer.EfClasses
+{
+    public class Book
+    {
+        public const int PromotionalTextLength = 200;
+        private HashSet<BookAuthor> _authorsLink;
+
+        //-----------------------------------------------
+        //relationships
+
+        //Use uninitialised backing fields - this means we can detect if the collection was loaded
+        private HashSet<Review> _reviews;
+
+        //-----------------------------------------------
+        //ctors
+
+        private Book() { }
+
+        public Book(string title, string description, DateTime publishedOn, 
+            string publisher, decimal price, string imageUrl, ICollection<Author> authors)
+        {
+            if (string.IsNullOrWhiteSpace(title))
+                throw new ArgumentNullException(nameof(title)); 
+
+            Title = title;
+            Description = description;
+            PublishedOn = publishedOn;
+            Publisher = publisher;
+            ActualPrice = price;
+            OrgPrice = price;
+            ImageUrl = imageUrl;
+            _reviews = new HashSet<Review>();       //We add an empty list on create. I allows reviews to be added when building test data
+
+            if (authors == null || !authors.Any())
+                throw new ArgumentException("You must have at least one Author for a book", nameof(authors));
+            byte order = 0;
+            _authorsLink = new HashSet<BookAuthor>(authors.Select(a => new BookAuthor(this, a, order++)));
+        }
+
+        public int BookId { get; private set; }
+        public string Title { get; private set; }
+        public string Description { get; private set; }
+        public DateTime PublishedOn { get; private set; }
+        public string Publisher { get; private set; }
+        public decimal OrgPrice { get; private set; }
+        public decimal ActualPrice { get; private set; }
+
+        [MaxLength(PromotionalTextLength)]
+        public string PromotionalText { get; private set; }
+
+        public string ImageUrl { get; private set; }
+
+        public IEnumerable<Review> Reviews => _reviews?.ToList();
+        public IEnumerable<BookAuthor> AuthorsLink => _authorsLink?.ToList();
+
+        public void UpdatePublishedOn(DateTime newDate)
+        {
+            PublishedOn = newDate;
+        }
+
+        public void AddReview(int numStars, string comment, string voterName, 
+            DbContext context = null) 
+        {
+            if (_reviews != null)    
+            {
+                _reviews.Add(new Review(numStars, comment, voterName));   
+            }
+            else if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context), 
+                    "You must provide a context if the Reviews collection isn't valid.");
+            }
+            else if (context.Entry(this).IsKeySet)  
+            {
+                context.Add(new Review(numStars, comment, voterName, BookId));
+            }
+            else                                     
+            {                                        
+                throw new InvalidOperationException("Could not add a new review.");  
+            }
+        }
+
+        public void RemoveReview(Review review)                          
+        {
+            if (_reviews == null)
+                throw new NullReferenceException("You must use .Include(p => p.Reviews) before calling this method.");
+
+            _reviews.Remove(review); 
+        }
+
+        public IStatusGeneric AddPromotion(decimal newPrice, string promotionalText)                  
+        {
+            var status = new StatusGenericHandler();
+            if (string.IsNullOrWhiteSpace(promotionalText))
+            {
+                status.AddError("You must provide some text to go with the promotion.", nameof(PromotionalText));
+                return status;
+            }
+
+            ActualPrice = newPrice;  
+            PromotionalText = promotionalText; 
+            return status; 
+        }
+
+        public void RemovePromotion() 
+        {
+            ActualPrice = OrgPrice; 
+            PromotionalText = null; 
+        }
+    }
+
+}

DataLayer/EfClasses/BookAuthor.cs

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+// Copyright (c) 2018 Jon P Smith, GitHub: JonPSmith, web: http://www.thereformedprogrammer.net/
+// Licensed under MIT licence. See License.txt in the project root for license information.
+namespace DataLayer.EfClasses
+{
+    public class BookAuthor
+    {
+        private BookAuthor() { }
+
+        internal BookAuthor(Book book, Author author, byte order)
+        {
+            Book = book;
+            Author = author;
+            Order = order;
+        }
+
+        public int BookId { get; private set; }
+        public int AuthorId { get; private set; }
+        public byte Order { get; private set; }
+
+        //-----------------------------
+        //Relationships
+
+        public Book Book { get; private set; }
+        public Author Author { get; private set; }
+    }
+}

DataLayer/EfClasses/LineItem.cs

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+// Copyright (c) 2018 Jon P Smith, GitHub: JonPSmith, web: http://www.thereformedprogrammer.net/
+// Licensed under MIT licence. See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+
+namespace DataLayer.EfClasses
+{
+    public class LineItem : IValidatableObject 
+    {
+        internal LineItem(short numBooks, Book chosenBook, byte lineNum)
+        {
+            NumBooks = numBooks;
+            ChosenBook = chosenBook ?? throw new ArgumentNullException(nameof(chosenBook));
+            BookPrice = chosenBook.ActualPrice;
+            LineNum = lineNum;
+        }
+
+        /// <summary>
+        /// Used by EF Core
+        /// </summary>
+        private LineItem() { }
+
+        public int LineItemId { get; private set; }
+
+        [Range(1,5, ErrorMessage =                      
+            "This order is over the limit of 5 books.")] 
+        public byte LineNum { get; private set; }
+
+        public short NumBooks { get; private set; }
+
+        /// <summary>
+        /// This holds a copy of the book price. We do this in case the price of the book changes,
+        /// e.g. if the price was discounted in the future the order is still correct.
+        /// </summary>
+        public decimal BookPrice { get; private set; }
+
+        // relationships
+
+        public int OrderId { get; private set; }
+        public int BookId { get; private set; }
+
+        public Book ChosenBook { get; private set; }
+
+        /// <summary>
+        /// Extra validation rules: These are checked by using the SaveChangesWithValidation method when saving to the database
+        /// </summary>
+        /// <param name="validationContext"></param>
+        /// <returns></returns>
+        IEnumerable<ValidationResult> IValidatableObject.Validate 
+            (ValidationContext validationContext)                 
+        {
+            if (BookPrice < 0)
+                yield return new ValidationResult($"Sorry, the book '{ChosenBook.Title}' is not for sale.");
+
+            if (NumBooks > 100)
+                yield return new ValidationResult("If you want to order a 100 or more books"+       
+                        " please phone us on 01234-5678-90",              
+                    new[] { nameof(NumBooks) });  
+        }
+    }
+
+}

DataLayer/EfClasses/Order.cs

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+// Copyright (c) 2018 Jon P Smith, GitHub: JonPSmith, web: http://www.thereformedprogrammer.net/
+// Licensed under MIT licence. See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using DataLayer.Dtos;
+using GenericLibsBase;
+
+namespace DataLayer.EfClasses
+{
+    public class Order
+    {
+        private HashSet<LineItem> _lineItems;
+
+
+        private Order() { }
+
+        public int OrderId { get; private set; }
+        public DateTime DateOrderedUtc { get; private set; }
+        public DateTime ExpectedDeliveryDate { get; private set; }
+        public bool HasBeenDelivered { get; private set; }
+        public string CustomerName { get; private set; }
+
+        // relationships
+
+        public IEnumerable<LineItem> LineItems => _lineItems?.ToList();
+
+        public string OrderNumber => $"SO{OrderId:D6}";
+
+        public static IStatusGeneric<Order> CreateOrderFactory(
+            string customerName, DateTime expectedDeliveryDate,
+            IEnumerable<OrderBooksDto> bookOrders)
+        {
+            var status = new StatusGenericHandler<Order>();
+            var order = new Order
+            {
+                CustomerName = customerName,
+                ExpectedDeliveryDate = expectedDeliveryDate,
+                DateOrderedUtc = DateTime.UtcNow,
+                HasBeenDelivered = expectedDeliveryDate < DateTime.Today
+            };
+
+            byte lineNum = 1;
+            order._lineItems = new HashSet<LineItem>(bookOrders
+                .Select(x => new LineItem(x.numBooks, x.ChosenBook, lineNum++)));
+            if (!order._lineItems.Any())
+                status.AddError("No items in your basket.");
+
+            status.Result = order;
+            return status;
+        }
+
+        public IStatusGeneric ChangeDeliveryDate(string userId, DateTime newDeliveryDate)
+        {
+            var status = new StatusGenericHandler();
+            if (CustomerName != userId)
+            {
+                status.AddError("I'm sorry, but that order does not belong to you");
+                //Log a security issue
+                return status;
+            }
+
+            if (HasBeenDelivered)
+            {
+                status.AddError("I'm sorry, but that order has been delivered.");
+                return status;
+            }
+
+            if (newDeliveryDate < DateTime.Today.AddDays(1))
+            {
+                status.AddError("I'm sorry, we cannot get the order to you that quickly. Please choose a new date.", "NewDeliveryDate");
+                return status;
+            }
+
+            if (newDeliveryDate.DayOfWeek == DayOfWeek.Sunday)
+            {
+                status.AddError("I'm sorry, we don't deliver on Sunday. Please choose a new date.", "NewDeliveryDate");
+                return status;
+            }
+
+            //All Ok
+            ExpectedDeliveryDate = newDeliveryDate;
+            return status;
+        }
+    }
+}